The goal of the proposed research is to provide a valid, reliable and functionally relevant quantification of the magnitude and direction of speech changes associated with BOTOX intervention for ADSD. Studies indicate that many patients with adductor spasmodic dysphonia (ADSD) exhibit improved speech production following BOTOX injection of the vocal folds. Instrumental analyses of acoustic and physiological variables have demonstrated post-treatment improvement on some variables (e.g., fundamental frequency variability), but deterioration on others (e.g., maximum phonation time). In addition, instrumental measures have revealed marked variability in response to treatment across individual patients. Because the precise relationships of instrumental measures to perceived speech qualities in ADSD remain unknown, the functional significance of the instrumental measures is difficult to interpret. However, studies that have attempted to assess functional improvement associated with BOTOX intervention have exhibited serious methodological limitations that raise questions regarding their reliability and validity. Two psychophysical scaling experiments will be conducted in which 16 highly trained normal adult listeners will judge the magnitude of deviations from normalcy of voice quality and fluency attributes of connected speech samples produced by ADSD patients, before and after BOTOX injection, in comparison to the speech of matched normal controls. Forty pre and post-BOTOX ADSD samples, selected from a preexisting data base of patient recordings, and 40 matched control samples will be presented for scaling using rigorously instrumented psychoacoustics laboratory procedures to control stimulus randomization, signal presentation, and recording of listener responses. The clinical voice and fluency characteristics of each pre-treatment ADSD speech sample will be extensively documented by a panel of experts. In addition, digital signal processing analyses including temporal, frequency and intensity measurements of the speech samples will be performed to determine the physical acoustic bases of perceived changes in speech attributes. Multivariate statistical models will be employed to relate perceptual and acoustic data before and after BOTOX injection. The proposed study will provide a critical, independent and functionally interpretable evaluation of BOTOX related speech changes in ADSD. As a result of this research, it may be possible to predict subtypes of ADSD patients likely to improve or decline on specific perceptual attributes based on pretreatment clinical characteristics.